The present invention relates to propeller shaft assemblies for motor vehicles. In particular, the invention concerns a center bearing tuned absorber support for a driveline propeller shaft assembly.
Constant velocity fixed joints are known in various designs. Such joints are used primarily in the driveline of a motor vehicle for driving the wheels of a motor vehicle. They can be used in either propeller shafts or in side shafts. Side shafts extend from the axle drive to the driven wheels. For example, they connect the output ends of the rear axle differential with the driven wheel hubs of the wheels. Propeller shafts serve to transmit the drive from the gearbox output of the front wheel drive unit to the rear axle differential associated with the rear axle.
As far as propeller shafts are concerned, a number of different designs are used. They may comprise, for example, two joints which are arranged at the end of a shaft connecting the two joints which serve to be connected to the gearbox output in front, and to the drive input at the rear. However, it is also possible to use a driveline consisting of several portions, for example, two propeller shaft portions between which there is provided a center bearing or intermediate bearing. Normally, at the ends of the propeller shafts, i.e., towards the gearbox output and the drive input, there are arranged universal joints. It is also possible for a universal joint to be provided in the central region. A constant velocity plunging joint can also be provided in the central region.
The drive unit of the motor vehicle generates vibrations which, in prior art assemblies, are transmitted to the propeller shaft in the form of movement vibrations and structure-borne sound. Moreover, vibrations are induced from the relatively high rotational speeds of the propeller shafts themselves. In addition, changing torque values and rotational speeds constantly occur during the transmission of the rotational movement throughout the driveline assembly. Load values suddenly increasing to 10 times the nominal torque, and rotational speeds up to 10,000 revolutions per minute are not rare.
To reduce the transmission of vibration and structure-borne sound to the vehicle compartment, the intermediate or center bearing of a multi-sectional propeller shaft is typically located at a nodal point along the propeller shaft assembly. In some vehicle designs, however, it would be desirable to locate the center bearing at a location other than a propeller shaft nodal point. For example, ground clearance and floor plan contour considerations may dictate a less than optimum location for the center bearing from a noise and vibration standpoint. Accordingly, there is a need for a propeller shaft center bearing support having tuned absorption characteristics to isolate driveline vibrations and noise from the vehicle compartment.
The present invention provides a center bearing tuned absorber. The center bearing tuned absorber assembly includes a cylindrical center bearing for supporting a rotating propeller shaft, and a tuned absorber having an inner sleeve disposed around the center bearing, and a mass-spring assembly arranged on an outer circumference of the inner sleeve. The mass-spring assembly includes a mass radially offset from, and attached to, the inner sleeve by a first damping element. The mass-spring assembly is arranged circumferentially on the inner sleeve in the direction of a first bending frequency associated with the rotating propeller shaft. The mass-spring assembly may be axially or radially offset from the center bearing.
In another aspect of the invention, first and second mass-spring assemblies are arranged on an outer circumference of the inner sleeve in the direction of respective vertical and lateral first bending frequencies of the rotating propeller shaft. Each of the mass-spring assemblies include a mass radially offset from, and attached to, the inner sleeve by a first damping element. The tuned absorber further includes an outer sleeve disposed around the inner sleeve, and a second damping element between the inner and outer sleeves.
The present invention is advantageous in that the center bearing tuned absorber can be located at numerous positions along the propeller shaft of a vehicle driveline and be configured to reduce or eliminate bending vibrations within the vehicle driveline.
Other advantages of the invention will become apparent upon to one of skill in the art upon reading the following detailed description and with reference to the drawings illustrating features of the invention by way of example.